Abstract: An arrangement for the underwater storage of environmentally hazardous waste, particularly radioactive or chemical waste, includes at least one secondary capsule (1) in the form of a cylindrical concrete body. The concrete body has a central, axially extending storage cavity (3). The cavity has the form of a shaft which is open at one end thereof and into which a waste-containing primary capsule (2) can be inserted, whereafter the open end of the shaft or cavity is sealed. Arranged in spaced relationship around the circumference of the concrete body (1) are a number of ballast chambers (4) which can be filled with water to varying degrees and the total, combined volume of the chambers is such as to enable the concrete body to be brought to a buoyant state, by emptying the chambers.